Automatic volume control for radio receiving apparatus



July 6, 1937. s. A. STEVENS ET AL ,0

AUTOMATIC VOLUME CONTROL FOR RADIO RECEIVING APPARATUS Filed Sept. 22,1934 2 Sheets-Sheet 1 III-l- Q INVENTORS Sydney Arthur Stevens 72mmATTORNEY and Lesgz'e Ernest Thongpsozz July 6, 1 93 7.

vs. A. STEVENS ET AL AUTOMATIC VOLUME CONTROL FOR RADIO RECEIVINGAPPARATUS Filed Sept. 22, 1934 2 Sheets-Sheet 2 SydneyAmlz INVEQITORSzuuS' evens and Les eEnne t7120122p'son. BY 51 1} THEIR ATTORNEYPatented July 6, 1937 UNlTED sr'ras PATENT orrics AUTOMATIC VOLUMECONTROL FOR RADIO RECEEVING APPARATUS tion of Pennsylvania ApplicationSeptember 22, 1934, Serial No. 745,146 In Great Britain September 30,1933 Claims;

This invention relates to automatic volume control for radio receivingapparatus and has for its object to provide improved arrangements foreifecting control of this character.

Automatic control of the volume ofthe reproduced signal inradio-receiving apparatus is usually efiected by varying the gridpotential relative to the cathode potential of one or more valves of theapparatus in accordance with the strength or amplitude of the receivedcarrier wave so as to render this grid potential increasingly negativeas the strength of the carrier wave increases and thus to reducecorrespondingly the degree of amplification of the valve which is beingcontrolled.

The variation of the grid potential of the controlled valve for thispurpose is generally effected by the provision of a resistance arrangedto be traversed by a direct current proportional to the strength of thecarrier wave, the potential thereby developed across this resistancebeing applied to the grid of the controlled valve and it has beenproposed to amplify this controlling potential by connecting a secondadditional resistance in the anode circuit of a valve upon the grid ofwhich a potential derived from the first resistance is impressed, theamplified controlling potential being derived from this secondresistance.

In radio-receiving apparatus embodying a detector of the dry surfacecontact type it is usual to connect a load resistance in the circuit ofthe detector and according to the principal feature of the presentinvention the potential across this resistance or any suitable portionthereof due to the rectified current traversing this resistance which isproportional to the strength of the carrier wave is arranged to beapplied to the grid of a valve of the apparatus, the current in theanode circuit of this valve being thereby correspondingly modified and apotential derived from this modified anode current being impressed uponthe grid of a Valve or valves so as to eifect an amplified volumecontrol of this valve or valves.

Preferably the valve to the grid of which the potential derived from theload resistance is applied is the valve from which the detector isimmediately supplied but this valve may be a valve preceding orfollowing the detector supply valve or may be a valve specially providedfor the purpose of amplifying the volume control potential derived fromthe load resistance.

Preferably a resistance is connected in the anode circuit of the valveabove referred to and the potential across this resistance or a portionthereof is utilized for varying the grid bias potential of the valve orvalves to be controlled.

The grid potential of the valves to be controlled by amplified automaticvolume control is determined by the difference of the potential dropsacross two resistances. By making one of these resistances carry asubstantially constant current such as the total anode current of allthe valves in the receiving apparatus other than the valve utilized foramplification of the volume control current it is possible to render thepotential drop across this resistance substantially constant. Thepotentials of the cathodes of all the valves except the amplificationvalve above referred to will thus be substantially constant and positiverelative to the H. T. negative terminal. The anode current of the valvewhich is utilized as an amplification valve for effecting volume controlis caused to traverse the other resistance before reaching the H. T.negative terminal and the potential of the positive-end of thisresistance will then vary with respect to that of the remaining valvecathodes in a'manner which will be an amplified reproduction of thepotential applied to the grid of this valve. The potential applied tothe grid of the valve to be controlled is thus the difference betweenthe potentials due to the potential drops in the two resistances.

The invention is illustrated by way of example in the accompanyingdrawings Figure 1 of which is a diagrammatic view showing the circuitsof a portion of a radio-receiving apparatus embodying one form of theinvention, Figures 2 and 3 being similar views of modified circuitsembodying other forms of the invention. Figure 4 is a diagrammatic viewof the complete circuits of a radio-receiving apparatus embodying astill further modification. 1

Referring now first to Figure 1 it will be seen that a portion of asuperheterodyne receiving apparatus is illustrated comprising an I. F.valve V! which may be the last of a series of I. F. valves and a valveV2 which may be the preceding I. F. valve in the series or the precedingH. F. valve. The valve VI is shown as comprising an anode l, a grid 2and a cathode 3 which is connected through resistances RI and R2 to thenegativeiH. T. terminal as shown, this terminal being connected to theearth conductor iof the apparatus through a resistance R3. The tunedcircuit of the anode I includes the primary winding 5 of a couplingtransformer Tl, the secondary winding 6 of which is connectedto adetector face contact type and a load'resistance R4 one terminal 'I ofthe resistance R being connected through a wire 8 to a point 9intermediate the resistances RI and R2.

The valve V2 similarly comprises an anode ID the tuned circuit of whichincludes the primary winding I I of a transformer T2, the grid I2 of thevalve V2 being connected through the secondary winding 53 of a couplingtransformer T3 and a wire I4 to a point I 5 intermediate the resistancesRI and R2. The cathode I5 of the valve V2 is connected through aresistance R5 to the earth conductor 4. An adjustable point in the loadresistance R4 is connected through wires II, I8 in series with thesecondary winding I9 of the transformer T2 to the grid 2 of the valveVI.

It will be understood that the provision of the resistance R3 causes thepotential of the earth suitable normal negative grid bias.

' When a signal is being received the mean potential of the grid I2 ofthe valve V2 will be the potential at the point I5 transmitted throughthe wire I l, and the mean potential of the grid 2 of the valve VI willbe theresultant of the potential of the point 9 and the potential of theadjustable point in the resistance R4 to which the wire I7 is connected.

As the signal strength increases the current traversing the loadresistance R4 will tend to increase but on the other hand the potentialapplied to the grid 2 from the resistance R4 by way of Wire Il willbecome more negative so that the anode current through the valve VI willtend to be reduced. This reduced current traversing the resistance R2will decrease the drop of potential in this resistance so that anincrease in the negative potential of the pointl will result and thispotential transmitted to the grid I2 of the valve V2 will reduce theanode current of this valve and thus eiiect the desired amplified volumecontrol. 7

It will be understood that the resistance R3 which is traversed by theanode currents of a number of the valves of the apparatus serves tomaintain a normal grid bias for the valves relative to the cathodesconnected to the earth conductor 4 and the potential at the point I5 isthus the resultant of the potentials due to the flow of currents in theresistances R2 and R3. 1

Referring now to Figure 2 a modified circuit arrangement similar to thatof Figure 1 is illustrated in which delayed amplified automatic volumecontrol is obtained by still further modifying the potential which isimpressed upon the grid or grids of the valve or valves to becontrolled.

For this purpose a resistance. R5 is connected in series with a drysurface contact rectifier M between the earth conductor 4 and the pointI5 intermediate the resistances RI and'R2. The wire I4 leading to thegrid or grids of the valve or valves to be controlled is in this caseconance RI, but in this case the magnitude of theresistancerR2 is suchthat when the valve VI is receiving a weak signal, (so thatthe voltagedrop across the resistance R4 is 'small theigrid bias on the 'grid 2 islow, and hence the anode current of the valve VI is relatively large)the voltage drop across the resistance R2 will be appreciably in excessof that across the resistance R3. Under these conditions the potentialof the point I5 will be positive relative to the earth conductor 4. Thefiow of current from the point l5 through the rectifier M in its reversedirection is however prevented by the rectifier so that since theresistance R5 is not being traversed by current the potential of pointI9 will be that of the earth conductor 4, and hence the only grid biasapplied to the preceding valves will be that resulting from the currentin their own cathode resistances, such as the resistance R5 in Fig. 1.For weal; signals, therefore, the amplified automatic volume control isinoperative, and is delayed until a signal is received of such magnitudethat the anode current of valve Vi is reduced to a value for which thepotential drop across the resistance R2 becomes the same or less thanthe potential drop across the resistance R3. When this occurs, currentwill flow from the earth conductor 4 through the resistance R5, therectifier M in its forward direction to the resistance R2. The

magnitude of the resistance R5 is so determined as to be much greaterthan the resistance in the forward direction of the rectifier M. Thepotential of the point I9 is therefore under these conditions verynearly equal to that of the point I5,

and any further increase in signal strength with 3 a correspondingreduction in the-anode current of the valve VI, will cause the volumecontrol potential transmitted by the wire I4 to be substantially that ofthe point I5, so that the negative value of this potential will increaseas the signal strength increases and will be an amplified reproductionof the grid control potential of the valve VI due to the action of theresistance R4. In the circuit of Figure 2, therefore simple automaticvolume control is applied to the valve VI, and delayed amplifiedautomatic volume control is applied to any desired preceding valves. Itwill be understood that instead of connecting the delay circuit it canif desired be arranged to operate prior to amplification in the circuitbetweenthe load resistance R4 and the grid 2 of the valve VI.

Additional amplification of the volumecontrol potential can be effectedby providing a resistance in the anode circuit of the controlled valveand deriving from thisresistance an amplified potential which is appliedto the grid of a preceding valve or valves so that a cascadeamplification action is obtained.-

Thevolume control termed quiet delayed automatic volume control can alsobe effected in receiving apparatus embodying the invention in thefollowing manner.

The amplified automatic volume control is effected as above described bythe variation in the drop of potential in the resistance connected inthe cathode circuit of the control valve such as VI, while the quietcontrol is effected by the change in the potential across a resistanceconnected in the positive side of the anode circuit of'the. valve.' Thispotential which is positive relative to the potential of the earthconductor 4 varies in magnitude to a greater extent than the rectifiedsignal voltage across the load resistance R4 on account of theamplifying action of the valve VI and may beused to control the gridbias potential applied to a L. F. valve, and by its considerablemagnitudeis suificient to vary the grid bias of the L. F. valve from avalue such thatthe valve passes no anode current at all, down to a pointat which the valve operates normally.

In a preferred arrangement for this purpose illustrated in Figure 3 asuitable resistance R6 is interposed in the connection between thepositive terminal of the H. T. source and the anode l of the detectorsupply valve VI utilized for amplification of the automatic volumecontrol, the anode terminal 20 of the resistance R6 being connectedthrough an adjustable resistance R? connected to earth at E to oneterminal 2i of a gas discharge tube N the other terminal 22 of which isconnected through a filter resistance R8 to the grid 23 of an L. F.valve V3 of the apparatus, the terminal 22 of the tube N being alsoconnected to the earth conductor 4 through a grid resistance R9.

It will thus be seen that under quiet conditions the grid 23 which isconnected to the earth conductor through the resistances R8 and R9 is atearth potential and by applying a positive potential to the cathode M anegative grid bias for the grid'23 is obtained.

The cathode 24 of the valve V3 instead of being connected directly tothe earth conductor 3 is connected to a point of positive potentialrelative to earth which is greater than the negative grid bias potentialnecessary to cause the valve V3 to take a zero anode current. Thispotential may be obtained in any suitable manner, and as shown in Figure3 the cathode 24 of the valve V3 is connected through a resistance RN]to a wire 25 which is connected to a point in the cathode resistance ofthe output valve or some other resistance in the apparatus in such amanner as to impress on the cathode 24 a suitable potential which ispositive relative to the potential of the grid 23.

When a weak signal is being received of insufiicient strength to beworth reproduction, the voltage drop across the load resistance R l willbe small and the valve VI will be operating at a low value of grid biaspotential determined by the resistance RI, sothat its anode current willbe relatively large and the potential of the terminal 20 will thereforebe low relative to the earth conductor t on account of the large voltagedrop across the resistance 6. Under these conditions the anode currentof the valve V3 will be zero and the valve will not therefore be able tooperate as an amplifier. Although therefore the H. F. and I. F.amplifying valves are working at their maximum sensitivity, there willbe no audio output from the loudspeaker. When a stronger signal is tunedin, the voltage drop across the load resistance R4 will increase, andthe potential of the grid 2 of the valve Vi will become more negativerelative to that of its cathode 3. The valve V I will thus operate toeffect simple automatic volume control in the manner above described andwill cause amplified automatic volume control to be applied to thepreceding valves.

As the anode current of the valve VI decreases the potential drop acrossthe resistance R6 will also decrease and the potential of the terminal29 will therefore become more positive relative to the earth conductor4. The gas discharge tube N connected in the anode circuit between theterminal 2B and the resistance R9 has the effect of preventing thepassage of current through this resistance until the potential of theterminal 20 increases to a predetermined value relative to the earthconductor 4 whereupon the tube N will become conducting and current willthen pass through the tube and through the resistance R9 to theearth-conductor 4. The flow of current through the resistance R9 willcause a drop of voltage therein rendering the upper end of theresistance R9 positive relative to the earth conductor l, this potentialbeing applied through the filter resistance R8 and its associatedcondenser as a grid bias to the grid 23 of the valve V3. The magnitudeof the resistance R9 is so proportioned that the grid bias will begreater than the excessive negative bias already applied to the valve V3as above explained. The grid bias or difference of potential between thegrid 23 and the cathode 2 E of the valve V3 can under'these conditionsbe arranged to be of the normal value for the valve to operate as anamplifying valve. A further increase in the strength of the receivedsignal will cause the anode current of the valve VI to be still furtherreduced and the potential of the terminal 28 will consequently beincreased,

thus causing an increase in the current traversing the discharge tube Nand the resistance R9. This increase of current would have the effect ofstill further reducing the bias of the valve V3 were it not for the factthat the resulting increase in the.

.the terminal it to a value sufficient to cause the discharge tube. N tobecome conducting, and hence the valve V3 will be operating on anexcessive negative grid bias and will not pass the V unwanted signal. Inorder to adjust the predetermined signal strength at which the controlshall become operative, the adjustable resistance R? is provided andthis resistance may either be connected between the terminal 26 andearth, as shown in Figure 3, or between the terminal 20 and the H. T.positive terminal depending partly on the characteristics of thedischarge tube employed, and also upon the H. T. voltages of 'the'receiving apparatus. It will be observed that the addition of this quietcontrol circuit in no way alters or-interferes with thesimple oramplified tautomatic volume control circuits or their operalOll.

The neon tube N may, if desired, be so mounted in the apparatus as to bevisible and will thus serve as .a tuning indicator in the well knownmanner.

Furthermore, if the valve immediately preceding the detector is arrangedto operate on the reflex principle, this valve will serve as an L. F.amplifier in addition to its other functions and the valve beingprovided with automatic volume control in-accordance with the inventionlow frequency automatic volume control will thus be obtained.

Referring now to the circuit arrangement for a superheterodyne receivingapparatus shown in igure 4 it will be seen that the aerial A is. coupledby means of a band-pass device B to circuit of a second I. F. valve VI.which serves asa supply valve for the detector D. The load resistance R4is connected through an L. F. transformer Tl to the grid circuit of anoutput valve Vl the anode circuit of which is arranged to supply currenttothe loud speaker (not shown) of the apparatus through a transformerTLS.

The rectifier D is connected in series with the load resistance R4 and aresistance RI I across the terminals of the secondary winding 6 of thetransformer TI and the terminal 25 of the resistance RII is connected bya wire 21 to an adjustablepoint 28 in a potentiometer resistance RI2 oneterminal of which is connected to the earth conductor 4 and the otherterminal to a point of suitable relatively low potential.

Theterminal 29 of the resistance RII is connected by means of a wire 30through a rectifier M2 in its reverse current direction to the point I5intermediate the resistances RI and R2 the point I 5 beingconnected to avolume control wire I4 which is connected to the grid circuits of thevalves V4 and V5 which are the volume-com trolled valves of theapparatus.

The anode I of the valve VI is connected through a condenser CI and adry surface contact rectifier M3 to the point 9 intermediate theresistances RI and R2, the-rectifier M3 being associated with a loadresistance S and a potentiometer resistance R13 connected between thepoint 9 and the H. T. positive terminal. The resistance RI3 enables adelay action to be obtained by applying an adjustable positive potentialto the lower end of the resistance S so as to bias the detector M3 andprevent the detector rectifying received signals of below apredetermined strength.

When signals of sufficient strength are received, a negative potentialis built up at the upper electrode of the rectifier M3,. this potentialbeing transmitted through a filter device consisting of a resistance RMand its associated condenser to the grid 2 of the valve VI, therebyapplying simple automatic volume control, and by the action of theresistances R2 and R3, as previously described, causing the valve VI tooperate as an amplifying valve to apply amplified automatic volumecontrol to the preceding valves. As regards obtaining the quiet controlaction a relatively large delay voltageis introducedinto the circuit ofthe second detector D, by connecting in the detector circuit aresistance RH across which a fall of potential is produced by tappingoff a positive potential from the upper end of resistance R2, which forweak signals is arranged to have a potential appreciably higher thanthat of the earth conductor 4, so that current will flow from the pointI5 through the rectifier M2, wire 39, resistance RI I, wire 2'5 to theearth conductor 4 through the potentiometer resistance RI 2. The effectof this current will be to make the point 29 positive relative to thepoint 26; some of ,the current in the circuit will therefore flowthrough the secondary winding 6, rectifier D and the resistance R4, asthe Whole of this circuit is in parallel with the resistance RI I. Ifthe magnitude of the current thus flowing is arranged to be sufiicient,the rectifier D will always be operating on its forward characteristic,and will not there fore rectify even though appreciably large signalsmay be generated in the windings of the at the aerial and should not bepermitted to reach the loud speaker. When a stronger signal is received,the efifect of the circuit including the rectifier M3 will'be to apply alarger control to valve Vi, and the point at which this control becomesoperative can be determined by the amount of delay introduced from thepotentiometer resistance RI3. One effect of this control voltage is toapply simple automatic volume control to the valve VI, a second effectbeing to apply amplified automatic volume control to the precedingvalves, and if desired this amplified volume control may be delayed by adelay circuit consisting of a rectifier M and a resistance R5 indicatedin dotted lines in Figure 4 and operating in the manner alreadydescribed. The third eirect of this control voltage, however, is toreduce the potential of the point I5 below that of the point 2%, so thatinstead of current flowing through the resistance R! I in the directionof the arrow, there is a tendency for the current to reverse. Therectifier M2 prevents this reversal, so that there is no longer any biasof either polarity applied to the circuit of the second detector D,which then operates in the normal manner. It will be evident that bysuitably proportioning the values of the resistances the detectorcircuit can be made to function at any desired signal strength.

In order to prevent a received signal of temporarily very low value dueto fading from failing to be transmitted, a condenser C of relativelylarge capacity is connected across the terminals of the resistance RI Ias shown.

The receiving apparatus of Figure 4 is shown asrprovided with terminalsP. U. for connection to the pick-up device of a gramophone and when theapparatus is being employed for the reproduction of gramophone recordsthe I. F. valve VI is utilized as a first L. F. amplifying valve in thewell-known manner, switches SI and S2 being under these conditionsadjusted from the positions shown in full lines to the positions shownin dotted lines.

In all the circuits'above described embodying the invention it will benoted that simplautomaticvolume control is arranged to be supplied to avalve such as the last I. F. valve which is 7 subject to a relativelyhigh voltage so that a high control potential cannot be impressedthereon without risk of distortion in operation. The amplified volumecontrol, on the other hand .is arranged to be applied to an earliervalve or valves of the receiving apparatus which being subject torelatively lower voltages is capable of having relatively high controlpotential im-' pressed thereon without distortion.

The invention is evidently not limited to the particular circuitconnections above described and illustrated by way of example which maybe varied in many respects without exceeding the scope of the invention.

Having now particularly described and ascertained the nature of our saidinvention and in what manner the same is to beperformed, we declare thatwhat we claim is:

1.In receiving apparatus embodying a plurality of electron amplifyingvalves and a detector the combination.'comprising, a first resistorconnected in the load circuit of saiddetector, a firstcircuit means toconnect at least a portion of said reistor' across the grid and cathodeof the valve immediately preceding the detector to effect simpleautomatic volume control for that valve, a current sourcehavingitspositive terminal connected to the anodes of said valves, a groundconductor connected to the cathode of each of the valves ahead of thevalve supplying the detector, a second resistor interposed between thenegative terminal of the source and the cathode of the valve supplyingthe detector, at third resistor interposed between the negative terminalof the source and said ground conductor to create a given potential forsaid conductor, and another circuit means connected with the grid of atleast one valve ahead of the valve supplying the detector and includingan asymmetric unit connected between the ground conductor and theterminal of said second resistor remote from the negative terminal ofthe source and said unit disposed with its forward direction toward saidterminal of the second resistor to effect delayed amplified automaticvolume control for said other valve.

2.,In receiving apparatus embodying a plurality of electron amplifyingvalves and a detector the combination comprising, a resistor connectedin the load circuit of said detector, circuit means to connect at leasta portion of the resistor across the grid and cathode of the valveimmediately preceding the detector to effect simple automatic volumecontrol for that valve, 2. current source for the anode circuits of'said valves, a second resistor interposed in the anode circuit of saidpreceding valve between the negative terminal of the current source andthe cathode, a third resistor interposed between the negative terminalof the source and the cathode of another one of said valves, and anothercircuit means including a fourth resistor and an asymmetric unitconnected between the terminals of said second and third resistor remotefrom the source to effect delayed amplified automatic volume control forsaid other valve.

3. In receiving apparatus embodying a plurality of electron amplifyingvalves and a detector the combination comprising, means to establish anormal negative grid bias potential for the valve immediately precedingthe detector, means including a first resistor interposed in the loadcircuit of said detector and having connection to the grid of saidpreceding valve to establish simple automatic volume control for thatvalve, a source of anode current for said valves, a second resistorinterposed between the negative terminal of the source and the cathodeof said preceding valve, a third resistor interposed between thenegative terminal of the source and the cathode of another one of saidvalves, said second and third resistor characterized by the normal potential drop across the third resistor being less than that across thesecond resistor, a connection including a fourth resistor and anasymmetric unit between the terminals of said second and third resistorremote from the current source and with the forward direction of saidunit toward the terminal of the second resistor, and means to connectthe terminal between said unit and the fourth resistor with the grid ofsaid other valve whereby delayed amplified automatic volume control forsaid other valve is effected.

4. In receiving apparatus embodying a first and a second electronamplifying valve and a detector the combination comprising, meansinterposed in the grid circuit each valve to effect a normal negativegrid bias potential, a source of current for the anode circuits of thevalves, a first resistor interposed between the negative terminal of thesource and the cathode of the second valve, a second resistor interposedbetween the negative terminal of the source and the oathode of the firstvalve, said resistors characterized by the normal potential drop acrosssaid first resistor being greater than that across said second resistor,a circuit connection including a third resistor and an asymmetric unitconnected between the terminals of said first and second resistorsremote from the source and with the forward direction of the unit towardthe terminal of the first resistor, means including a resistor in theload circuit of the detector for applying a potential between theterminal of the first resistor remote from the source and the grid ofsaid valve, and other means to connect the terminal between said unitand the third resistor with the grid of the first valve.

5. In receiving apparatus including a high frequency amplifying valve, adetector and a low frequency amplifying valve the combinationcomprising; a first resistor interposed in the load circuit of thedetector, means to connect at least a portion of said resistor with thegrid of the high frequency tube to effect automatic volume control ofthat valve, a second resistor interposed in the anode circuit of saidhigh frequency valve, means to establish a normal negative grid biaspotential for the low frequency valve and characterized by effectingsubstantially normal zero anode current of that valve, circuit meansincluding a resistor and a gas discharge tube connected between theterminal of said second resistor toward the anode of the associatedvalve and the grid of the low frequency valve, and means including asource of alternating signaling current connected with the grid of thehigh frequency valve to vary the potential of said grid with respect tothe cathode in accordance with said signaling current whereby thepotential applied to said circuit means is varied to modify the normalnegative grid bias potential of the low frequency valve to effectamplification of the output of the detector.

6.In receiving apparatus embodying a high frequency valve, a detectorand a low-frequency valve the combination comprising; a grid circuit forthe low frequency valve connected between the grid and a groundconductor, said circuit including two resistors and a windinginductively coupled with the output of the detector, means connectedbetween the cathode of the low frequency tube and such ground conductorto effect a quiet grid bias that gives substantially zero anode current,a resistor and a winding serially interposed in the anode circuit of thehigh frequency valve with said winding inductively coupled with theinput of the detector, means including a source of alternating signalingcurrent connected with the grid of the high frequency valve, and anothercircuit means including a discharge'tube connected between the terminalof the last mentioned resistor toward the anode of the high frequencyvalve and the mid terminal of the two resistors of the grid circuit ofthe low frequency valve whereby the potential effected by the current ofthe anode circuit of the high frequency valve on said discharge tube inresponse to said signaling current is operative to modify the grid biasof the low frequency valve.

7. In receiving apparatus embodying a high frequency valve, a detectorand a low frequency valve the combination comprising; a grid circuit forthe low frequency valve including a winding coupled with the output ofthe detector, means including a source of potential connected with saidgrid circuit and characterized by establishing a quiet grid biaspotential that effects substantially zero anode current, and anodecircuit for the high frequency valve including a winding coupledwith'the'inp ut of the detector, means including a source of alternatingsignaling current connected with the grid of the high frequency valve,and a circuit means including a discharge tube connected between a pointof varying potential of the anode circuit of the high frequency valveand the grid circuit of the low frequency valve to modify the quiet gridbias potential in response to the signaling current applied to the highfrequency valve whereby amplification of such signal'energy afterdetection is effected. V

8. In receiving apparatus including a high frequency amplifying valve, adetector and a low frequency valve the combination comprising; a firstcircuit means including a source of alternating signaling currentcoupled with the grid circuit of the high frequency valve, a secondcircuit means including a first and a second resistor as well as thedetector and a winding, said winding coupled with the anode circuit ofthe high frequency valve to inductively receive an electromotive forcein response to the amplified signaling current, grid circuit means forsaid low frequency valve and including said first resistor,

and other circuit means including a rectifier and a current sourceconnected across said second resistor, said rectifier disposed to passcurrent which flows in said second resistor in a direction opposite tothat supplied through the detector in' response to the electromotiveforce induced in the winding of said second circuit means whereby thedetector operates on its forward characteristic and quiet automaticvolume control for the low frequency valve is effected. V

9. In receiving apparatus including a high fre-' quency amplifyingvalve, a detector and a low frequency valve the combination comprising;a

first circuit means including a source of alternating signaling currentcoupled with the grid circuit of the high frequency valve, asecond'circuit meansincluding a first and a second resistor as well asthe detector and a winding, said winding coupled with the anode circuitof the high frequency valve to inductively receive an electromotiveforce in response to the amplified signaling current, a third circuitmeans including a first rectifier and a load resistor connected betweenthe anode and cathode of the high frequency valve, said rectifierdisposed with its forward direction toward the cathode, means to connectsaid load resistor with the grid of the high frequency valve to effectautomatic volume control for said valve in response to variationseffected in the current supplied to the anode of said valve, gridcircuit means for said low frequency valve and including said firstresistor,

and a fourth circuit means including a second rectifier and a currentsource connected across said second resistor, said second rectifierdisposed to pass current which flows in said second resistor in adirection opposite to that supplied through the detector in response tothe electromotive force induced in the winding of said second circuitmeans whereby the detector operates on its forward characteristic andquiet automatic volume control for'the low frequency valve is effected.V

10. In receiving apparatus including a first stage and a second stagehigh frequency valve, a detector and a low frequency valve thecombination comprising; a first circuit means including a source ofalternating signaling current coupled with the grid circuit of the firststage high frequency valve, a second circuit means including a first anda second resistor as Well as the detector and a winding, said windingcoupled with the anode circuit of the second stage high frequency valveto inductively receive an electromotive force in response to theamplified signaling current, a third circuit means including a firstrectifier and a load resistor connected between the anode and cathode ofsaid secondstage valve, said rectifier disposed with itsforwarddirection toward the cathode, means to connect said load resistorwith the grid of said second stage valve to effect automatic volumecontrol for that valve in response to variations effected in the currentsupplied to the anode of said second stage valve, a source of currenthaving its positive terminal connected with the anodes of said valves, aground conductor connected with the cathode of said first stage valve, athird and a fourth resistor connected between the cathode of said secondstage valve and the negative terminal of said current source, a fifthresistor interposed between the ground conductor and the negativeterminal of the current source, means to connect the mid terminal of thethird and fourth resistors with the grid of said first stage valve toeffect amplified automatic volume control for that valve in response tovariations effected in the current supplied to the anode of said secondstage valve, grid circuit means for said low frequency valve andincluding said first resistor, and a fourth circuit means including asecond rectifier and a current source connected across said secondresistor, said second rectifier disposed to pass current which flows insaid second resistor in a direction opposite to that supplied throughthe detector in response to the electromotive force induced in thewinding of said second circuit means whereby quiet automatic volumecontrol for the low frequency valve is effected.

SYDNEY ARTHUR STEVENS. LESLIE ERNEST THOMPSON.

